If you did not un-derstand the ciphering algorithm yet

1:fI uoy did ton dnatsrednu eht gnirehpic mhtirogla tey

2:fI uoy did ton nu-dnatsred eht gnirehpic mhtirogla tey

3:fI uoy did ton nudnatsred eht gnirehpic mhtirogla tey

So which is correct???Help me,thank you.